Stereochemistry — 3D Arrangement of Atoms
Chirality: A molecule is chiral if it has a non-superimposable mirror image. A chiral center (stereocenter) has 4 different groups attached.
Enantiomers: Mirror images of each other. Same physical properties except optical rotation. Rotate plane-polarized light in opposite directions: R (+, dextrorotatory) and S (−, levorotatory).
R/S configuration:
Assign priority (highest atomic number = 1) to all 4 groups
Orient lowest priority away from you
If 1→2→3 is clockwise = R; counterclockwise = S
Diastereomers: Stereoisomers that are NOT mirror images. Different physical properties. Can have multiple stereocenters.
Meso compounds: Has stereocenters but is achiral due to internal plane of symmetry.
Fischer projections: 2D representation of stereochemistry. Horizontal lines come toward viewer; vertical lines go away.
Biological relevance: Enzymes are stereospecific — they bind only one enantiomer. Drugs often have one active enantiomer. Thalidomide: one enantiomer treats nausea, the other causes birth defects.
Reference:
TaskLoco™ — The Sticky Note GOAT
